[LUM#5] Discovering the Universe

[LUM Magazine] - Published on March 28, 2017 in Science-Society

December 2013: the sun discovers a new satellite. The latest addition is called Gaia. Its mission: to explore a galaxy that is as close as it is unknown, our own. And to help us better understand the universe...

50 billion pieces of data: that's what the European Gaia satellite, which explores the outer reaches of our galaxy, sends us every day. It took no less than three years to begin deciphering this enormous mass of information, thanks to complex software, some of which was designed by the Montpellier Laboratory of Universe and Particles (LUPM). Your computer would have taken hundreds of years to complete this task...

Mapping the galaxy

Comfortably positioned around the "Lagrange point"1.5 million kilometers away from us—the precise location in the Sun-Earth system where the gravitational forces of the two bodies are balanced—Gaia observes, catalogs, and calculates. And it helps us make giant leaps forward in our knowledge of the Milky Way. Most of the objects observed by the satellite were previously little known: "Gaia has collected data on 1.15 billion stars. That's huge! Until now, we only knew the distances of about 100,000 stars," enthuses Gérard Jasniewicz, an astronomer at LUPM.

The primary objective of the Gaia mission is to measure the positions, distances, and movements of celestial objects within the galaxy. The stakes are high: "The goal is to create the most accurate three-dimensional map ever obtained. And thus to understand the very structure of our galaxy," explains Fabrice Martins, also an astronomer at LUPM.

A galaxy that remains largely unknown. Why? First of all, because it is gigantic. To give you an idea of its size, if we could travel at the speed of light, it would take us about 100,000 years to cross it from one end to the other... "With Gaia, we will be able to accurately map all the bright stars in our galaxy located within 30,000 light-years,"explains Gérard Jasniewicz.

Time machine

One reason why so little is known about the Milky Way is because we are part of it. "It's paradoxical: in some respects, we know less about the Milky Way than we do about other galaxies," Fabrice Martins continues. " We lack the necessary perspective to form an overall picture. Many stars are hidden from us by clouds of gas and dust that form a curtain impenetrable to telescopes."

Brightness, position, speed of stars: based on this fundamental data, the European satellite and its multiple instruments (see box) have much to teach us. In this immense undertaking, the task assigned to LUPM is crucial: to study the "radial velocities" of stars—their speed of approach or recession. "Gaia will also reveal the intrinsic brightness of stars, and therefore their mass: this is crucial data for characterizing them," continues Fabrice Martins.

A way to learn more about these brilliant populations—blue, white, yellow, orange, red, dwarf, giant, supergiant stars, etc.—that populate our galaxy. Many researchers at LUPM, who are working on star classification, eagerly await these results, which will enable them to verify hypotheses, models, and theories. They are not alone. Gaia is inspiring the global scientific community, which will have free access to all the project's data. And which hopes to see new horizons opening up soon in many disciplines...

New horizons

Gaia is not only an explorer and cartographer of our galaxy, but also its archaeologist. The speeds, movements, but also the age of stars and their chemical compositions: all these elements provide valuable insights into the galaxy's past and how it was formed. "A telescope is a time machine!" sums up Gérard Jasniewicz.

At the end of its mission, which is scheduled to last until 2020 but could well be extended, the Gaia satellite will have advanced our knowledge in all areas, opening our eyes to many subjects: quasars, exoplanets, asteroids, other galaxies, and more. This galactic encyclopedia will even make it possible to verify the effects of universal gravitation on a very large scale. And thus to test the fundamental laws of physics. An encyclopedia so vast that scientists are already rejoicing at the wealth of subjects it offers for study... and which remain to be explored.

Keywords: LUM#5, LUM Magazine